How to Extract All Files from a Specific Directory in a Zip File Using Java?

Question

How can I unzip all files from a particular directory within a zip file in Java?

ZipFile zipFile = new ZipFile("path/to/your.zip");
Enumeration<?> entries = zipFile.entries();
while (entries.hasMoreElements()) {
    ZipEntry entry = (ZipEntry) entries.nextElement();
    if (entry.getName().startsWith("specific/directory/")) {
        InputStream stream = zipFile.getInputStream(entry);
        // Use stream to read/write the contents to the destination
    }
}

Answer

Unzipping files from a specific directory within a zip file is a common task in Java, particularly when you want to focus only on certain contents without extracting everything. This guide explores how to achieve that using the Java `java.util.zip` package.

import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;
import java.io.InputStream;
import java.io.FileOutputStream;
import java.io.File;

public class UnzipExample {
    public static void main(String[] args) throws Exception {
        ZipFile zipFile = new ZipFile("path/to/your.zip");
        Enumeration<?> entries = zipFile.entries();
        String targetDir = "output/directory/";

        while (entries.hasMoreElements()) {
            ZipEntry entry = (ZipEntry) entries.nextElement();
            if (entry.getName().startsWith("specific/directory/")) {
                File newFile = new File(targetDir, entry.getName());
                new File(newFile.getParent()).mkdirs(); // Create necessary directories
                InputStream stream = zipFile.getInputStream(entry);
                FileOutputStream fos = new FileOutputStream(newFile);
                byte[] buffer = new byte[1024];
                int len;
                while ((len = stream.read(buffer)) > 0) {
                    fos.write(buffer, 0, len);
                }
                fos.close();
                stream.close();
            }
        }
        zipFile.close();
    }
}

Causes

Not all files are extracted when the entire zip file is unzipped.
Need to organize extracted files by specific directories within the zip structure.
Avoid unnecessary file extraction to save time and resources.

Solutions

Use the `ZipFile` class to access the zip file.
Iterate through each entry of the zip file and check if the entry starts with the desired directory path.
Read the input stream and save the contents where required.

Common Mistakes

Mistake: Not creating the output directory before writing files.

Solution: Ensure that you create all necessary directories using `mkdirs()` method before writing the output files.

Mistake: Forgetting to close streams and files, leading to memory leaks.

Solution: Always close your InputStream and FileOutputStream in a finally block or use try-with-resources.

Helpers

Java unzip specific directory
extract files from zip Java example
Java zip file operations
unzip files Java
Java zip file handling